Method and apparatus for continuously determining the oxygen content of gases



March 11, 1969 DO ET AL 3,432,404

METHOD AND APPARATUS FOR CONTINUOUSLY DETERMINING THE OXYGEN CONTENT OF GASES Filed May 7, 1965 GAS OUTLET INVENTORS [Mf/P/CH 52 96.9

United States Patent 3,432,404 METHOD AND APPARATUS FOR CONTINUOUSLY ggggMINING THE OXYGEN CONTENT OF Emerich Erdiis and Jiri Bares, Prague, Czechoslovakia, assignors to Ceskoslovenska akademie ved, Prague, Czechoslovakia, a corporation of Czechoslovakia Filed May 7, 1965, Ser. No. 453,951 Claims priority, application Czechoslovakia, Apr. 23,

1964, 2,375/ 64 US. Cl. 204-1 8 Claims Int. Cl. B01k 3/04; G01m 7/00 ABSTRACT OF THE DISCLOSURE This invention relates to a method and apparatus for the continuous determination of oxygen concentration in gases and more particularly to such improved method and apparatus having a relatively short delay of response.

In controlling the combustion of solid, liquid and gas eous fuels in metallurgical, chemical and other technical processes, there is required a reliable method of rapidly, accurately and continuously determining the concentra tion of oxygen in combustion gases. Analysis of the constituents in fuel combustion is most important to maintain, by preventing excessive fuel consumption, an operation under optimum economical conditions, to permit the elimination of operational failures and to prevent formation of explosive mixtures. Furthermore, in addition to the need for continuously determining the concentration of oxygen in combustion processes, such method is of great value in other productive and research fields such as microbiology, organic chemistry and the like.

There are known at present many types of devices for analyzing and testing gas mixtures for oxygen concentration and for monitoring fuel consumption. In one type of such devices: the operation is based upon the electrical measurement of thermal gas conductivity; in another type of analyzers the operation is based upon the selective absorption of gas in liquids. Further, there are known infra-analyzers and paramagnetic oxygen content analyzers. These known continuous analyzers donot provide necessary selectivity in process-monitoring, they are generally not sufiiciently reliable in operation and have a relatively slow response, i.e., a relatively long inertial period or delay.

In addition to the above outlined devices, there have also been utilized electrochemical analyzers of oxygen concentration in gases. Such analyzers operate on the principle of an oxygen electrode in an alkaline medium. However, this type of analyzer does not lend itself to practicable application since the sensing element included therein has a very short lifetime in the presence of acidic gases (such as the carbon dioxide by-prod uct) formed in the process. Furthermore, in this latter type of analyzer the electrical signal provided by the sensing element indicates the rate of gas flow rather than being directly proportional to the oxygen content.

Accordingly, it is an important object of this invention to provide an improved method of continuously automat- 3,432,404 Patented Mar. 11, 1969 ically monitoring the oxygen content in a gas mixture; said method is selective for oxygen, reliable in operation and substantially reduces the delay in indicating oxygen concentration as compared to known methods used for the same purpose.

It is another object to provide an improved, accurate and more durable apparatus for performing the method set forth hereinbefore.

Briefly stated, in accordance with the invention, there is provided a method for automatically continuously ascertaining the oxygen content in a gas comprising the steps of applying to an electrode immersed in an electrolyte solution having a maximum pH value of substantially 1, a potential from a potential source having a value which is negative with respect to the potential required to evolve hydrogen at the electrode, and subjecting the immersed electrode to the gas to depolarize it with the oxygen in the gas and to produce an electric current flowing from the source to the electrode, the intensity of the. current being a function of the oxygen content of the gas.

Also in accordance with the invention, there is provided an apparatus for automatically ascertaining the oxygen content in a gas comprising a given electrolyte having a maximum pH value of substantially l, a hollow electrode structure closed at one end and comprising a chosen electrode material, immersed at its closed end in the electrolyte. A potential source is included having a value which is negative with respect to the potential required to evolve hydrogen at the chosen electrode material immersed in the given electrolyte, and means are provided for applying the aforesaid potential to the electrode.

For a better understanding of the invention together with other and further objects thereof, reference is had to the following description taken in conjunction with the accompanying drawing.

The drawing shows partly in structural section a preferred, although exemplary embodiment of the invention.

Referring now to the drawing, the apparatus includes a battery 11 which may suitably be of the acidic lead storage type filled with sulfuric acid of a concentration of 30% by weight and having a positive electrode 12 and a negative electrode 13. Electrode 12 and 13 are respectively connected to the terminals of a potentiometer 14 from which a predetermined voltage is taken off by means of a slider. In an exemplary application, a suitable voltage taken from potentiometer 14 may be 175 millivolts, such voltage being more positive than the potential of negative electrode 13. The voltage taken from potentiometer 14 is applied over a variable resistor 15 to an indicating electrode generally indicated at 16. The voltage across the variable resistor 15 is continuously measured by a suitable measuring device 17, such as a millivoltmeter.

The indicating electrode 16 comprises a hollow, substantially tubular insulating body 16a closed at one end by an electrode base 20 and having an opening at the other end to receive a tube 16b which functions as a gas inlet. The body 16a is further provided with a lateral opening which functions as a gas outlet. The electrode base 20 is made of a porous material such as graphite. Within the electrode body 16 there is disposed a silver wire 19 through the potential is applied to electrode base 20. The indicating electrode 16a extends into the interior of battery 11 where it is immersed in the sulfuric acid electrolyte thereof. A rubber bushing 18 is provided forming a seal between the battery wall and the body 16a. The graphite body of electrode base 20 may be coated with paraflin to render it hydrophobic.

A basic principle in the operation of the invention is the application of a potential to indicating electrode base 20 which is negative with respect to the potential required to evolve hydrogen, such potential is hereinafter designated as a negative potential.

When the apparatus is connected in circuit, initially the indicating electrode base 20 is depolarized by the oxygen in the gas entering the electrode 16. Thereafter, current flows from the tapped point on potentiometer 14 through variable resistor 15 to indicating electrode 16, the intensity of the current flow is measured as a voltage by the millivoltmeter 17. The source of the negative potential and indicating electrode 16 are connected in circuit with a constant, although adjustable resistance; the indicating electrode 16 is supplied with the negative potential from electrodes 12 and 13 which, suitably designated as auxiliary electrodes, are reversable and regeneratable, and are immersed in the same solution as the indicating electrode 16. The negative potential may also be provided either completely or partly from an external potentiometer to which one or both auxiliary electrodes are connected.

The outside of indicating electrode 16 is in contact with the electrolyte solution of battery 11, while its inside is in contact with the gas to be analyzed. The material of electrode base is suitably so chosen that in a given electrolyte solution it has a hydrogen evolution voltage which is greater than the potential applied to the indicating electrode 16.

The indicating electrode base 20 is advantageously associated with a catalyst which accelerates the reaction on the indicating electrode. For this purpose the wire 19 is preferably made of silver.

The apparatus constructed in accordance with the principles of the invention permits a continuous determination of the oxygen content in a gas stream flowing through electrode 16. With this apparatus, the time necessary to obtain a 90 percent response ranges from a few tenths of one second to, at most, a few seconds. This continuous determination is fully automatic and the obtained elec trical signal is sufficiently strong to permit even a direct connection of an indicating device. In such connection, the scale of millivoltmeter 17 is directly calibrated in terms of a gaseous mixture having a known oxygen content and the indicating scale may easily be adjusted to a desired range with a potentiometer.

The invention contemplates the use of a generally acidic electrolyte solution having a pH not exceeding 1. Thus the deleterious effects of acidic gases such as carbon dioxide, which are experienced in known devices are eliminated. Due to the reversibility of auxiliary electrodes 12 and 13, they are readily regenerated by direct current supplied thereto, either periodically between relatively long time periods, or continuously by connecting them to a potentiometer fed from an external source.

By rendering the indicating electrode base 20 hydrophobic with respect to the electrolyte solution, e.g., by means of a paraffin coating on the graphite body, it is protected from choking or flooding and thus its life expectancy is extended without adversely affecting its function.

The method and apparatus described hereinabove may be advantageously utilized in the determination of oxygen in gases produced by the oxidation of fuels with air or oxygen at high temperatures and with the release of intense heat. They may also be employed in the analysis of the oxygen content in gases produced by flamentation mechanisms in fermentation processes, in chemical syntheses, and in all cases where it is necessary to continuously ascertain the oxygen content in a gas. They may be used to ascertain abrupt changes in oxygen content. The two-sided indicating electrode 16, constructed in accordance with the invention, is particularly advantageously adapted to function as a sensing element in automatic recording instruments and is utilizable in a wide range of oxygen concentrations from as low as a few percents.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A method of automatically and continuously ascertaining the oxygen content in a gas comprising the following steps: deriving a potential from a potentiometer connected between the positive and negative electrodes of a storage battery containing an electrolyte having a maximum pH value of substantially 1 in which said positive and negative electrodes are immersed, applying said potential through a variable resistance to an indicating electrode immersed in said electrolyte, said potential being negative with respect to the potential required to evolve hydrogen at said indicating electrode, and exposing said indicating electrode to said gas to depolarize it with the oxygen in said gas and to generate an electric current flowing from said potentiometer to said indicating electrode, the intensity of said current being a function of the oxygen content of said gas.

2. A method as defined in claim 1 wherein said indicating electrode includes a hollow body closed at one end by a porous base comprising graphite, said hollow body contains a silver catalyst, at least a portion of said base being immersed in said electrolyte.

3. A method as defined in claim 2 wherein said indicating electrode is at least partially hydrophobized.

4. An apparatus for automatically and continuously ascertaining the oxygen content in a gas comprising a battery having a positive and negative electrode immersed in an electrolyte having a maximum pH value of substantially 1, an indicating electrode immersed in said electrolyte, said indicating electrode including a hollow body closed at one end by means of a base comprising a porous electrode material, the outside of said base being exposed to said electrolyte by being immersed thereinto, a potentiometer connected between said positive and negative electrodes, means for deriving from said potentiometer a potential having a value negative with respect to the potential required to evolve hydrogen at said electrode material immersed in said electrolyte, a variable resistor, and means for applying said potential to said indicating electrode through said resistor to generate an electric current which, when the inside of said base is in contact with said gas, has an intensity which is a function of the oxygen-content in said gas.

5. An apparatus as defined in claim 4 including a catalyst contained within said indicating electrode for accelerating the reaction thereon.

6. An apparatus as defined in claim 5 wherein said catalyst includes silver.

7. An apparatus as defined in claim 4 wherein said electrode material is graphite.

8. An apparatus as defined in claim 4 wherein said base is at least partially rendered hydrophobic.

References Cited UNITED STATES PATENTS 2,651,612 9/1953 Haller 204- 2,805,191 9/1957 Hersch 2041.1 2,898,282 8/1959 Flook et a1 204-195 2,939,827 6/1960 Jacobson et al. 204-195 3,160,577 12/1964 Nolan 204-195 3,179,581 4/1965 Lewin et al 204195 3,291,705 12/1966 Hersch 204-l.l 3,296,113 1/1967 Hansen 204195 JOHN H. MACK, Primary Examiner.

T. TUNG, Assistant Examiner.

US. Cl. X.R. 204-195, 277, 278 

